This invention relates to a solid-state laser device for emitting a plurality of laser beams by the use of a single laser medium. Such a plurality of laser beams will be collectively called a multi-laser beam.
A laser device of the type described is known which is capable of emitting a multi-laser beam by the use of a single laser medium. By way of example, such a laser device is disclosed in a book which is written by Alexander A. Kaminskii and which is published 1981 by Spriger-Verlag under the title of "LASER CRYSTALS", pages 111 to 113, Section 3.18 Multibeam Crystal Laser. As shown in FIG. 3.52a of the above-mentioned book, the laser device comprises the laser medium and four mirrors located around the laser medium. The laser medium is disposed in first and second resonance optical paths which pass through the laser medium with first and second medium lengths, respectively. A first pair of the mirrors is placed in the first resonance optical path with the laser medium put therebetween while a second pair of the mirrors is placed in the second resonance optical path with the laser medium put therebetween. The first pair of the mirrors forms a first resonator while the second pair of the mirrors forms a second resonator. Along the first resonance optical path, a first excitation laser beam is supplied to the laser medium from a first excitation laser beam source to excite the laser medium while a second excitation laser beam is supplied along the second resonance optical path to the laser medium from a second excitation laser source to excite the laser medium. Each of the first and the second excitation laser beams may be supplied from semiconductor laser elements.
The first resonator cooperates with the laser medium to pump the laser medium and to generate a first output laser beam which is derived from the laser medium as one of the multi-laser beam. Similarly, the second resonator cooperates with the laser medium to pump the laser medium and to generate a second output laser beam which is derived from the laser medium as another multi-laser beam. In this event, the first output laser beam has a first wavelength which is equal to about 1.06 micronmeters while the second output laser beam has a second wavelength which is equal to about 1.35 micronmeters. In the laser device, each of the first and the second laser beams is excited by the four-level system and may therefore be a fourth level laser beam. This is because each of the first and the second medium lengths is determined such that emission can be excited by the four-level system.
With this structure, no consideration is made at all about oscillation of a plurality of different level laser beams by the use of a single laser medium. Accordingly, it is impossible to generate a blue-colored laser beam which is very important for the production of three primary colors.